1. Field of the Invention
This invention relates to the field of radio frequency interference (RFI) suppression, and particularly to systems and methods for suppressing RFI in wired transmission systems.
2. Description of the Related Art
The performance of wired data transmission systems can be degraded by RFI which originates from local amateur radio operators. For example, a high-speed Internet access system employing VDSL modems might occupy a bandwidth of up to 12 MHz; amateur radio bands are allocated frequency bands between 1.8 MHz and 30 MHz. A signal received by the modem is typically fed to the input of an analog-to-digital converter (ADC). Due in part to poor balance of the twisted pairs making up the data transmission system, RFI from a local ham operator can be coupled into the ADC input. The RFI power may be 10–20 dB larger than the received signal power, thereby significantly degrading the dynamic range of the ADC.
Some modems employ a receive (RX) filter designed to attenuate any signals beyond 12 MHz. However, such filters are generally less than 100% effective; as such, RFI due to amateur radio frequencies between 1.8 MHz and 30 MHz can adversely affect modem performance.